Which is the best book which one should refer to, for preparation of DILR section of CAT (Arun Sharma or Nishit Sinha or any other book of your preference)? Please elaborate it as well by keeping in mind the understanding and explanation level of book, coverage of important topics and sufficiency.

Here are few books.
Data Interpretation and Logical Reasoning Books For CAT:

1.A Modern Approach to Logical Reasoning( by R.S. Agarwal)
This CAT book by R.S. Agarwal is to start with the most basic reasoning problem as it is quite simple to understand. It is segregated into different sections such as logic, statements, inferences and arguments, assumptions, conclusions, course of actions, logical puzzles, etc.

2.How to Prepare for Logical Reasoning for CAT book (by Arun Sharma)
This book by Tata McGraw Hill contains all topics to be considered under Logical Reasoning for CAT as well as other entrance exams. Each topic is explained with solved examples followed by a series of problems with varied difficulty levels to solve which gives an individual enough practice for this section.

3.How to Prepare for Data Interpretation for CAT book (by Arun Sharma)
This book focuses on all areas of Data Interpretation and Data Sufficiency. It provides and emphasizes on developing our calculations to get an edge with DI. This book also provides you with previous years questions, Model and Sample test papers.

4.Logical Reasoning and Data Interpretation for the CAT (by Nishit Sinha)
This book covers fundamental and advanced topics under the aforementioned section which are explained with the help of solved examples, case lets and exercises to do. It is useful for various other exams as well.

5.Data Interpretation (by Nishit Sinha)
Practice Book for CAT and Other MBA Entrance Examinations( by Nishit Sinha):
This book provides adequate practice and to sharpen the skills for Data Interpretation. It is also quite useful for other competitive exams like NMAT, GMAT, SNAP, XAT, CMAT, etc.